Internet protocol (IP) telephony systems often complete calls to non-customers via one or more publically switched telephony networks (PSTNs), and via one or more cellular service providers. It is common for an IP telephony system to contract with multiple different telephony carriers, all of which are capable of terminating a call to the same telephone number. Thus, the IP telephony system often can choose which carrier it wishes to use to terminate a call.
Because an IP telephony system has choices, the IP telephony system monitors the quality provided by the different carriers it uses to terminate communications. If the quality provided by a particular carrier falls below a minimum acceptable level, the IP telephony system stops terminating calls through that carrier, and instead routes calls through an alternate carrier.
An IP telephony system also routes calls based on the price charged by the telephony carrier to terminate the calls. All other things being equal, the IP telephony system routes a call through the carrier that charges the least to terminate the call.
Some telephony carriers are quite large and are capable of terminating calls to many different telephone numbers. Because of their size and reach, it is common for an IP telephony system to route a large volume of calls through a large carrier.
Other carriers are quite small and are capable of terminating calls to only a small group of telephone numbers. Because of their smaller size and reach, it is common for the IP telephony system to route only a small volume of calls through a small carrier. However, often a small carrier is able to terminate calls for a lower cost than one of the large carriers. Thus, provided the small carrier can provide acceptable call quality, it is often desirable to route a call through a small carrier to obtain the lower termination rate.
Some telephone numbers, or groups of telephone numbers, are intrinsically impaired. This means that there is some problem that prevents any carrier, regardless of its size or capabilities, from terminating calls to those numbers and providing consistently high call quality.
If a small carrier is completing calls to numbers that are intrinsically impaired, the call quality metrics for those calls necessarily will be poor. And because the small carrier only handles a relatively small volume of calls, the poor call quality for calls to the intrinsically impaired telephone numbers will cause the average call quality values for the small carrier to appear relatively poor. Because of this, the IP telephony system will tend to stop routing calls through the small carrier.
Because the small carrier is no longer being used, calls to the intrinsically impaired numbers are instead routed to one of the large carriers. When a large carrier completes calls to the intrinsically impaired numbers, the quality of those calls will still be poor—because the telephone numbers are intrinsically impaired. But because the poor quality metrics for calls to the intrinsically impaired numbers will be averaged against a large volume of calls to numbers that are not intrinsically impaired, the overall average call quality metrics for the large carrier will still appear to be good. Thus, the IP telephony system will continue to terminate calls to the intrinsically impaired numbers through the large carrier.
As noted above, the large carrier could charge a higher rate to terminate calls than the small carrier. Because of the above factors, the IP telephony system could end up paying more to complete the calls to the intrinsically impaired telephone numbers through a large carrier than it would have paid to complete the calls through a small carrier, even through the quality of the calls is the same.